1.3. Bonding - Comparing Melting Points

Question 1

Describe the structure and bonding in Mg

Answer 1

Giant metallic lattice
Electrostatic attraction between positive metal ions and delocalised electrons

Question 2

Describe the structure and bonding in MgCl₂

Answer 2

Giant ionic lattice
Electrostatic attraction between oppositely charged ions

Question 3

Describe the structure and bonding in Si

Answer 3

Macromolecular
Covalent bonds between atoms

Question 4

Describe the structure and bonding in CH₄

Answer 4

Simple molecular
Covalent bonds between atoms
Intermolecular forces between molecules

Question 5

What bond or force is broken when simple molecular structures are melted or boiled?

Answer 5

Weak intermolecular forces

Question 6

Why don’t the covalent bonds break when simple molecular structures are melted or boiled?

Answer 6

Covalent bonds are much stronger than intermolecular forces, so the intermolecular forces break first

Question 7

Why does Na have a lower melting point than Mg?

Answer 7

Mg²⁺ ions have a higher charge than Na⁺
Mg²⁺ ions are smaller than Na⁺ ions
There is a stronger attraction between the positive ions and delocalised electrons in Mg

Question 8

Why does Na have a higher melting point than K?

Answer 8

• Both are giant metallic lattice
• Na⁺ ions are smaller than K⁺ ions
• There is a stronger attraction between the positive ions and delocalised electrons in Na

Question 9

Why does NaCl have a lower melting point that Na₂O?

Answer 9

• Both are giant ionic lattice
• O²⁻ has a greater charge than Cl⁻
• There is a greater attraction between the oppositely charged ions in Na_2O

Question 10

Why does NaCl have a higher melting point than KCl?

Answer 10

• Both are giant ionic lattice
• Na⁺ ions are smaller than K⁺ ions
• There is a stronger attraction between the oppositely charged ions in NaCl

Question 11

Why does diamond have a higher melting point than Ca?

Answer 11

• Diamond: Macromolecular, covalent bonds between atoms
• Ca: Giant metallic lattice, attraction between positive ions and delocalised electrons
• Covalent bonds are stronger than metallic bonds and require more energy to break

Question 12

Why does graphite have a higher melting point than KCl?

Answer 12

• Graphite: Macromolecular, covalent bonds between atoms
• KCl: Giant ionic lattice, attraction between oppositely charged ions
• Covalent bonds are stronger than ionic bonds and require more energy to break

Question 13

Why does silicon have a higher melting point than oxygen?

Answer 13

• Si: Macromolecular, covalent bonds between atoms
• O₂: Simple molecular, intermolecular forces between molecules
• Intermolecular forces are weaker than covalent bonds and require less energy to break

Question 14

Why does lithium have a higher melting point than HCl?

Answer 14

• Li: Giant metallic lattive, attraction between positive metal ions and delocalised electrons
• HCl: Simple molecular, intermolecular forces between molecules
• Intermolecular forces are weaker than metallic bonds and require less energy to break

Question 15

Why does AlCl₃ have a higher melting point than CH₄?

Answer 15

• AlCl₃: Giant ionic lattive, attraction between oppositely charged ions
• O₂: Simple molecular, intermolecular forces between molecules
• Intermolecular forces are weaker than ionic bonds and require less energy to break